Research On Structural Performance Of Prestressed Concrete Beams At Low Temperatures

In order to study the mechanical properties of steel strand that used in prestressed concrete beams,tensile tests were performed to obtain the stress-strain curves of steel wires in strand at different low temperatures.Empirical prediction formulae were developed to incorporate the influence of low temperatures on mechanical properties of steel wires.Based on the stress-strain curves of single wire,theoretical and numerical models were developed to predict the mechanical properties of multi-layer steel strands.Based on the test and analysis results,empirical models were developed to predict the mechanical properties of steel strands at different low temperatures including the elastic modulus,yield and ultimate strengths.This offers useful means to calculate the mechanical properties of steel strands at low temperatures.In order to study the structural performance of the bonded and unbounded prestressed concrete(PC)beams at different low temperatures,the numerical models were proposed.The accuracies of these numerical models were validated against the test results.Based on the validated finite element(FE)model,the parametric studies were performed.The main parameters,i.e.,low temperature,reinforcing ratio of nonprestressed reinforcement and prestressed reinforcement,effective tensile stress,strength of concrete,span-depth ratio and bonded or unbounded.Based on the experimental data and the FE numerical results,the theoretical calculation methods of cracking loads and ultimate loads of bonded and unbonded prestressed concrete beams were proposed.Based on the experimental data of freeze-thaw cycles of concrete,the constitutive equations of concrete after freeze-thaw cycles and the mechanical properties of concrete were proposed.With the validated FE model,this parametric studies on PC beams after freeze-thaw cycles were carried out,which provided a certain reference for engineering practice.